The role of dissolved silica on the biodegradation of octylamine

Dissolution of aquifer-associated mineral solids such as silica may affect the natural bioattenuation of organic compounds by altering their chemical speciation and thus their biodegradability. A study was conducted to evalua te the effect of dissolved silica on the rates of biodegradation of a catio nic surfactant, octylamine, by Rhodococcus erythropolis. The presence of di ssolved silica or a surrogate added by dissolving sodium metasilicate signi ficantly enhanced the biodegradation rates of octylamine. Microbial kinetic studies based on the Monod/Haldane equation indicated that the rate enhanc ement was caused by a decrease in the inhibitory properties of octylamine, rather than by an improvement in buffering of the medium. In the presence o f dissolved silica, mu(max) and K-s remain virtually unaffected, but the in hibition constant, K-i, increased several orders of magnitude (from K-i = 1 .32 mM in the silica-free system to K-i > 10(6) mM in the silica system). S urface tension studies suggested that the presence of dissolved silica sign ificantly decreased the surface-activity of octylamine.